1. Field of the Invention
The present invention relates to an intermediate transfer ink jet recording method and a device for practicing said method, and more particularly to an ink jet recording method comprising forming an ink image on an intermediate transfer medium by ink jet recording and transferring the ink image to a recording medium, and a device for practicing said method.
2. Background Art
An ink jet recording system is advantageously excellent in the simplicity of the mechanism and noiseless. This type of printing, however, has problems including that the quality of prints varies depending upon the kinds of recording media, for example, the quality of recording paper and the image of a portion remaining undried of an ink image is disturbed during the discharge of the recording medium.
In order to solve such problems, a proposal has been made on a method called an "intermediate transfer system" wherein an ink image is once formed on a transfer medium by an ink jet recording system and then transferred to a recording medium (see U.S. Pat. Nos. 4,538,156 and 5,099,256). In this method, the recording head can be disposed apart from the recording paper. Consequently, this method has a feature that it is possible to prevent the contact of the recording head with the recording paper caused by the disposition of the recording head in close proximity to the recording paper or the clogging of the recording head attributable to the collection of paper lint on the recording head.
The above-described device should satisfy both a requirement that a desired ink image is accurately formed on an intermediate transfer medium and a requirement that the ink image is transferred to the recording medium under low pressure with a good efficiency. With respect to the former requirement, if ink droplets ejected on the intermediate transfer medium are excessively spread or flowed on the intermediate transfer medium to cause a remarkable variation in the location or shape thereof, the resultant print is unfavorably disturbed. In the present specification, this phenomenon is often referred to as "repelling" of the ink. For example, FIG. 9 schematically shows a straight line printed by a group of dots. When a group of dots as shown in FIG. 9(a) is formed onto an intermediate transfer medium, a good print can be provided on a recording medium. On the other hand, as shown in FIG. 9(b), when there occurs the "repelling" phenomenon wherein a dot is excessively broadened or flowed outside a region indicated by a broken line where the dots are to be formed, no good print can be provided on the recording medium. With respect to the latter requirement, printing cannot be effected with a high efficiency if the ink image remains on the intermediate transfer medium or if a high pressure is necessary for the transfer.
Japanese Patent Laid-Open No. 146750/1989 discloses a method which comprises forming a thin film of glycerin on a transfer medium and forming an ink image of an oil-base ink on the thin film. According to this method, it is possible to accurately form an ink image and to transfer the ink image to the recording medium under relatively low pressure with a high efficiency.
However, the present inventors have confirmed that, when this method is effected by using a water-base ink composition containing water as a main solvent, in some cases, the transfer cannot be often effected with a high efficiency as opposed to the oil-base ink.
Furthermore, in the conventional recording method, a linear load (the force per unit length) of about 2.5 kg/cm may be required. If it is possible to effect the transfer under lower pressure, the limitation on the material for constituting the device can be eliminated, so that a device having a lower weight and a smaller size could be realized.